Corrosion resistant flame reactor



Nov. 5, 1968 J. E. LOEFFLER ET AL 3,409,407

CORROSION RESISTANT FLAME REACTOR Original Filed Jan. 8, 1965 INVENTORS. JOHN EDWARD LOEFFLER,JR.

BY HP. MCALISTER PAUL PROKISH United States Patent Shamrock Corporation, a corporation of, Delaware f Continuation of application SerLNo'. 424,418, Janff8,

application'July 31,1967, Ser. No. 667,021:

ABSTRACT OF THE DISCLOSURE In producing acetylene by incomplete oxidationof sa turated hydrocarbons, where a portion of a gas distributor issues streams of premixed oxygen plus hydrocarbon feedstock into a reactionzone, and other portions oftthe distributor feed streams. of auxiliary oxygen into the reactionrzone, it has also .been disclosed to provide the lower portion of the distributor adjacent the re action'zone with a liquid-cooled heat exchanger. This. exchanger passes cooling fluid around the lower. portion of the means feeding the. gaseous streams into the reaction zone and as a resultthe exchanger-has a lower tube sheet exposed on One Side to the reaction chamber and on the other to the cooling fluid. The sheet thus encounters an extreme heat flux while at the same time is exposed to the deleterious atmosphere of thereaction zone- To withstand this atmosphere and to cope with the extreme heat flux, the lower tube sheet is made from low-carbonsteel having a thin chromium diffusion layer of chromium dilfused into the surface of the sheet cXpQSedto the reaction chamber. 7

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of copending U.S. application Ser. No. 424,418, filed Jan. 8, 1965, and now abandoned.

BACKGROUND oF THE INVENTION In a typical method for the production of acetylene,

3,409,407 Patented Nov. 5, 1968 permanently positioned flame in the flame chamber. For consistent operation, it is necessary that the flame be maintained in the same region-of the flame chamber and of roughly the saine si'z'e and temperature. This stabilization, of the flame canbe accomplished bythe introduction ofauxiliary streams of oxygen through ports in the gas distributor itself, such ports typically being directed to anangle from the vertical so that the oxygen streams impinge upon the streams of the gaseous oxygen-hydrocarbon. mixturej'An example of a gas distributor unit to which the present'invention may be applied is disclosed in U'.S.'Patent 3,285,707. This mode of operation, in addition to providing enhanced amounts of oxygen within the reaction zone,causes the production of small,- localized flame 'cones of high heat radiation in that portion of the flame cliamber near'est the gas dist-ributor. The result-is an extremely high heat flux on the surface of the distributor apparatus. In fact, flame temperatures in this region approach 500 F. and the heat flux on the surface of the gas distributor is in excess of 1,000,000 B.t.u. per square foot per hour.

Provision may be made for dissipating much of this heat by constructing the gas distributor such that the portion nearest the flame chamber is provided with metal conduits surrounding the ends of the tubular gas channels, through which conduits is passed a cooling fluid such as water. While this cooling fluid circulation is effective for the maintenance of the gas distributor at a reasonable temperature, the effect of the same on the surface of the gas distributor facing the flame chamber is to create severe thermal stresses therein. These stresses may ultimately result in the cracking of the gas distributor surface.

It is further believed that a problem encountered in the the flame chamber is the result of the fact that a substantial amount of carbon (in the form of soot) is produced in the flame reaction. This carbon, in combination with the other gases present, affords a canbu-rizing atmosphere which diffuses carbon into metal surfaces exposed to the reaction chamber, thereby embrittling such surfaces and deleteriously affecting their resistance to thermal stresses. Thus, if a low-carbon steel is used for the construction of a gas distributor, the surface of the distributor is concluding higher molecular weight acetylenes, tars, aro- 1 "matics such as naphthalene, indene and analogous compounds, and a substantial amount of soot. This mixture is immediately quenched with water to arrest the cracking reaction and is then passed to a number of quenching and purification steps wherein the acetylene is recovered and the impurities are removed.

To promote proper combustion of the gas mixture and for other purposes, there is interposed between the mixing chamber and the flame chamber a gas distributor unit. This apparatus ordinarily comprises a cylindrical burner block or the like containing regularly spaced tubular channels passing from the mixing chamber into the flame chamber. The gas passes through these channels at a speed in excess of the flame propagation speed of the hydrocarbon-oxygen mixture. Thus, the distributor section functions also as a flame arrestor by preventing the backup of ignited gases from the flame chamber into the mixing chamber.

A major problem encountered in the use of the abovedescribed apparatus is the maintenance of a stable and verted' to high-carbon steel after a relatively short period of use.

Because such high-carbon steels are extremely hard and brittle, carburization increases the susceptibility of the surface to cracking as a result of the thermal stresses. On'the other hand, use of a less carburization-susceptible steel alloy such as stainless steel is undesirable because the thermal conductivity of such alloys is substantially lower than that of ordinary carbon steel. Thus, the temperature difference between the flame chamber-facing surface of the gas distributor and the interior thereof is considerably greater, and consequently the thermal stresses are greater and cracking is more likely.

SUMMARY OF THE INVENTION A principal object of the present invention, therefore, is to provide an improved metal surface for the portions of the flame chamber subject to high heat fluxes, which surface is resistant to cracking as a result of thermal stresses and is also resistant to carburization.

A further object is to provide a metal surface for hightemperature work which combines the advantages of carburization resistance characteristic of stainless steel and other steel alloys with high thermal conductivity which is a characteristic of non-alloy low-carbon steel.

Other objects will in part be obvious and will in part appear hereinafter.

It has been discovered that the foregoing objects can be attained by providing, on the surface of the gas distributor exposed'totheflame reaction, such-gas;distri.b tor being.'constructediof low-carbon steel, acsurface-of elemental chromium whichis diffused into the low-carbon Stee1 "=,,i;. r- '1' i 1. '1 "in Examples of gas distributor units to awhigthflthe .\present invention may be applied I are'tdisclosed and iclairnedz-in the followirigiUzS; Patentsv- 3,-28-5,707:,-3;2s5,70s, and -3, 287-;090.=These' units are similar in designpand the pnesenf invention will be described in terms ofthe apparatus tributor"'unittzas disclosedinsUstrPatent 3;285,'707and as contemplatedtin='eonnectien -witlr the present invention. Numeralil ihdieates emixing chamber wheneirr the-hydrocarbon and oxygenLfed from means not shown are mixed and preheated. The gaseous-mixturethen-passes-through the/gas distfib'utofapparams -via distributor= tubes 2' t flame chamber-"4'?-Distributor tubes Q, thrugh aportion o'f their le'ngth, may be' surrounded by suitable -insu'lating orr'efrac'tory' material in the 'spaces si 'lhe lower'port'ion of th'e'-gas-distributor is-fitted with anupper metal' sheet 6,- and intermediate metal 'sheet 8, and a lower metal'tube sheet 7, through which the distributor tubes 2 pass, and which sheets thereby-form a double-pass shell-and-tube heat exchanger through which a coolant such as water is passed, the coolant entering the exchanger through conduit 9 from coolant supply means not shown and DESCRIPTION OF THE PREFERRED EMBODIMENTS In order that heat shall be readily carried from the flame chamber through the walls of the gas distributor to the cooling fluid, the gas distributor is constructed'of low-carbon steel. But, on the surface of lower tube sheet 7 facing the reaction chamber, chromium is diffused into the low-carbon steel thereby preparing a chromium diffusion surface by a process known to those skilled in the art as chromizing.

The chromizing process involves heating a metal object in the presence of a chromium material, for example a compound having a relatively high vapor pressure which is reduced to metallic chromium during chromizing. At the high chromizing temperatures chromium contacting the surface of the metal workpiece diffuses into the surface of the object being treated.

Suitable chromizing methods described in the prior art which are useful for producing the apparatus of this invention include the particularly eflicient and useful method described in US. Patent 3,152,007, i.e., contacting the workpiece to be chromized at a temperature of between about 13002000 F. with a gaseous chromium halide. US. Patent 3,152,007 shows that although the chromium halide can be a mixture of chromium chlorides, such halide can be simply chromic chloride which is passed into contact with the workpiece by a transmitting gas, such as hydrogen, for reduction of the vaporized chromic chloride to form gaseous chromous chloride and elemental chromium which diffuses into the surface of the workpiece thereby preparing the chromium diffusion surface within the treated workpiece.

;*;A1SQ'BmO1'1g-{ the prior art ethods whicha areparticularlyaeflicient.:andruseful forvzchrornizing, and. which are thus=useful'fortproducingthe apparatus of this invention, isthe-method :described in .U.S..'Patent3,021,231, i.e., contacting the: workpiece with; a solid chromium=providr ing material-insrmixture with a halide-containing substance at-a temperature suitably in the range. ofv 1650+2400- ;F. to provide diffusioncoatings of chromium. within the. surface of low carbon steel upto a depth of diffused .chro' mium of about 0.019 inch. Although US. Patent 3,152,?- OOT diSCIOS 'S" thes'ol id chromium=providing material can be 'elemental 'etiromium;: U-.S. Patent 3,021,231 -employs ferro chrome containiiig atleast-30 weight-#perqe'nt chrohiiuni a's the'j solidtbhromium providing"material and as the lialide' containing "substance employs a chromous" or chrome halide? or 'for -e'xamp'le'ga hydrogen halideg' or rmetanie san 'su c'ii as iron chloridejor an activator such as annatiiiipmuaiiueidr sodium or potassiurh-bifluoride. By fapplyirig "a 'thindaye'r'bf "e'llfi'e'ii'tal 'chro'r'niilni-di-ffiu sed"into"'the flame-eiiposed", law-carpet] steel s'urfaceof tlie' gas distrib utor' it 'isipo's'sibleto render; this 'surface essentially impe'rv to the"atmospher'existirig in the chamber during the acetylene-forming'reactio'ri;' At

a rie, the 'sa fie time, because theresulting'surface i extrerrie ly thin it does 'not noticeably deerease the thermal con'du'ctiiv'itylo f the'low-carb'on steel gas distributor. Therefore, the high he f flu'xes across the ifacfofthedistributor'do no'tcause ckirig foi 'otherdeterioration.

It is to bet understood that the inventiohfi s not' limited by t'he "e rnbodiments described hereinabove, but includes such chang'e's and modifications as may be app rent to one skilled in theai't upon' reading the appended claim. 1 iw ina [ii ":1 '1. In:v an apparatusfor thlep'roductio'n of acetylene b'y incomplete oxidation of saturated, hydrocarbonsin a flame r ac i n .su hab a ehavins I Qa mixing chantbefftqr said hydrtp ca rb'or s and oxygen, 1a flame chamber into which a'plurality of auxiliary .streams of oxygen are introduced to .stabiliie the .positionof. said flame,

a gas-distributor sect on rntercpninejcting said chamliers, and hayinga pluralityof tubular channels opening intogsaid mixing chamber and said flame chamber,

a liquid-cooled heat exchanger interposed. between .said

mixing chamber and said flame chamber, said .ex- I ,-,changer having a, metal. tube sheet ,forming one boundaryofisaidfiame chamber andsurrounding the mportion of said. tubular channels ,opening ,into said flame chamber, and means positioned within said exchanger for introducing said plurality of auxiliary streams of oxygen into said flame chamber through perforations in said tube sheet between adjacent groups of the openings of said tubular channels into said flame chamber, the improvement in said apparatus comprising a lowcarbon steel metal tube sheet for said liquid-cooled heat exchanger having a surface exposed to said flame chamber of low-carbon steel containing chromium diffused within said steel to a depth of not substantially above about 0.019 inch and provided by contacting a low-carbon steel tube sheet on at least said surface, at a temperature of between about 1300-2400 F., with a composition comprising a compound selected from the group consisting of gaseous chromium halides, and solid chromium-providing material in mixture with halide-containing substance.

No references cited.

JAMES H. TAYMAN, 111., Primary Examiner. 

